System for the installation of electrical cables

ABSTRACT

A system for installation of electrical conductors in buildings, comprising a flat cable having a base with open grooves in which bare conductors may be inserted, further comprising cable ducts or channels into which such cables may be introduced, which ducts may be attached to a wall or may be suspended on a ceiling in a building, and further comprising contact means which may be detachably clamped in a cable duct, said contact means having contact pins or strips which contact the conductors of such a cable when this contact means is clamped in the cable duct.

United States Patent 1191- Attema Nov. 6, 1973 [54] SYSTEM FOR THE INSTALLATION OF 2,267,610 12/1941 Lavone 339/21 R ELECTRICAL CABLES 3%??83? 13%33? l fim "533721 13 ou e a. 75 lnvento Gusbertus Attema Gornch m, I 1 r Netherlands l e FOREIGN PATENTS OR APPLICATIONS 284,707 1 1965 N th 1 d 339 21 R 1 Assigneel 8 NM, 1,261,306 441961 FZmZZ 33921 R Gormchem, Netherlands 206,960 1 1960 Germany 339 21 R [22] Filed: Jan. 24, 1972 Primary ExamInerMarv1n A. Champ1on PP NOJ 219,996 Assistant Examiner-Robert A. Hafer Attorney-Smyth, Roston & Pavitt [30] Foreign Application Priority Data 1 R Jan. 26; 1971 Netherlands 7100995 [57] P ACT June 11,1971 Netherlands 7108031 A for "181151113110" of elecmcal Conductors? bu1ldmgs, comprismg a flat cable having a base mm 52 us. c1. 339/21 R, 339/44 Open grooves in i h bare conductors y e 511 1m. 01 H01r 9 00 Serted, further comprlsmgpable ducts Oflchannels mm [58] Field of Search 339/ 14, 20-24, Whlch sllch Cables y b9 Introduced, Whlch ducts Fl y 339/36 37 44 be attached to a wall or may be suspended on a ceIlIng v in a building, and further comprising contact means [56] References Cited which may be detachably clamped in a cable dnct, said UNITED STATES PATENTS 7 contact means hav1ng contact plus or strIps wh1ch con- 3 422 387 1/1969 S t t l 339,21 R tact the conductors of such a cable when this contact pngmgs e a v. 2,361,721 10 1944 Van Deventer 339/21 R means clamped m the cable duct 2,192,899 3/1940 Edmonson 339/21 R 27 Claims, 15 Drawing Figures PATENTEDNUV 6 I975 SHEET 2 BF 3 Fig 7 Fig,

SYSTEM FOR THE INSTALLATION OF ELECTRICAL CABLES The invention refers to the installation of electrical conductors.

According to the preferred embodiment'of the inven-.

abutment with the base of the U, the inside of the legs.

of the U are provided with ribs behind which the base element rests when inserted into the duct, for retaining the base element therein; the slots in the base element are open to the open portion of the U and the legs of the U have additional ribs near or at the respective ends of the legs which face each other. Contact support means are provided and constructed to be received in the duct, above the base element therein, and they have outwardly extending, resilient, positioning members for engagement behind said additional ribs to retain the support means in the duct and in definite position relative to the base element therein; plural contact pins or strips of rectangular cross section and flat end faces are held in the support means and extending therefrom in aligned position with the conductors in the grooves of the base member. Resilient means, preferably individual springs, urge the individual contact pins through the slots in the base member and into contact making engagement with the respective conductors therein, and maintain the contact making engagement.

While the specfication concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the in vention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a cross-section of a base for receiving electrical conductors;

FIG. 2 is a cross-section of a cable duct with a base and conductors according to FIG. I placed therein;

FIGS. 3 and 4 are cross-sections of other cable ducts in accordance with the invention, that of FIG. 3 being a support for a ceiling and that of FIG. serving as a hollow skirting board;

FIG. 5 is a fragmentary cross-section of an assembly of base, conductors and a cable duct incorporating means for making electrical contact with the conductors;

FIG. 6 is an isometric view, partly in section, of a device for making electrical contact with the conductors;

FIGS. 7 and 8 show respectively a plan and a side elevation of another contact device;

, FIGS. 9A and 9B are sections of twocontact-strip holders for the contact device of FIGS. 7 and 8;

FIGS. 10A and 10B are respectively a fragmentary cross-section and a fragmentary cross-section to a much enlarged scale, of a complete contact device of which the portion shown in FIGS. 7 and 8 forms part;

FIG. 11 is a longitudinal section through the contact device of FIG. 7 to which a cable duct has been connected; and

FIGS. 12 and 13 are cross-sections of a modified base with conductors.

Referring now to the drawings, a cable-base element or casing in accordance with the invention shown in FIG. 1 comprises a lower part 1 of an electricallyinsulating resilient plastics material having grooves 2 each communicating with the upper surface of the part 1 through a respective slot 3. Naked solid or braided conductors can be received in the grooves 2 and are insulated from each other by the intervening parts 4 of the lower part 1. The width of the slots 3 can be less than the transverse dimensions of the conductors, since the conductors'can be pressed into the grooves 2 by utilizing the elasticity of the plastics material. It is also possible to place insulated conductors in these grooves, for example telephone or bell wires.

A cover part 5 is connected along one longitudinal edge to the lower part 1 by means of an intermediate thinner part 6 acting as a hinge. Towards the other edge the cover part5 has an integral rib 7 with a beaded free edge. The rib 7 is connected by means of a further part of reduced thickness 8 to a projection 9 and to an engaging strip 10 which strip in the relaxed state, forms a straight extension of the cover part 5. That one of the grooves 2 situated farthest from the cover part 5 communicates with the upper surface of the lower part through a groove 3' which groove is shaped to receive the beaded edge of the rib 7. The end surfaces of the lower part 1 are so shaped that they augment the inherent flexibility to facilitate introduction into a cableduct.

FIG. 2 shows the base of FIG. 1 installed in a cableduct 11. The duct is shaped as a substantially U- section. The base of this section is provided with longitudinal outwardly-extending projections or ridges 12 which are preferably continuous and in which the heads of fixing screws can be received without projecting. Further, the section has inwardly-extending ribs 13 at the free edges as well as with other ribs 14 parallel thereto and each spaced inwardly from the respective free edges. The duct 11 is preferably an extended plastics section. After the conductors have been placed into in the grooves 2, the cover-part 5 is closed so that the head of the rib 7 is received by in the groove 3 and the cover part 5 is thus retained on the lower part 1. The edge of the lower part 1 adjacent to the hinge 6 is engaged behind one of the longitudinal ribs 4 of the duct, and the bottom part 1 is then pressed into the duct 1 1, so that the opposite edge if snapped behind the other longitudinal rib 14. The projection 9 rests against the side of the duct carrying the other rib so that the engaging strip 10 is bent upwardly. This strip can then readily be grasped in order to re-open the cover, as required for example when contact is to be made with the conductors 15, for which purpose a portion of the cover can be cut away.

FIG. 3 shows a cable-duct similar to that of FIG. 2, comprising a substantiallyU-shaped section 16 and an integral substantially Cshaped section 17. The section 17 is shaped to receive a junction piece 18 of a suspension rod, which piece is placed longways into the opening of the section 17 and engaged therein by turning through a quarter turn. At the face of the section 16 opposite to that at which the C-section is arranged, an external beaded rib 19 is provided on to which supports for ceiling-panels can be clamped. The section 16 is provided with longitudinal ribs 13 and 14 in like manner to the cable duct of FIG. 2.

The cable-duct of FIG. 4 is similar to that of FIG. 3 but is further provided, below the section 16, with one or more additional U-sections 16' of smaller dimensions for example, for accommodating low tension cables or branch cables. This cable-duct can be closed off with a cover 20 which has, in this embodiment, a transverse flange 21 secured to the section 17 by a screw 22 screwed into a member 23-. At the lower edge of the cover 20 integral claws 24 or a longitudinal hooked flange engages behind a rib 13' provided at the free edge section 16. The cover may alternatively be closed by a snap-lock.

FIG. shows a device for making electrical contact I with the conductors received in the grooves 2 and comprises a support fitted between the end ribs 13 of one of the sections according to any one of FIGS. 2, 3 and 4. The support 25 has retractable resilient positioning members 26 which can engage behind the rib 13. These resilient members 26 can be formed in various ways as will be described in more detail hereinafter. Preferably, as shown, these members are bevelled at the underside and provide support by their inherent resiliency, so that the support 25 of the contact members can simply be pressed past the ribs 13 into the cable-duct. If necessary the U-section can be provided with additional ribs 14 on which additional members 26 can engage.

Contact-strips 28 pass through holes 2 in the support and are biased by springs 29, which strips, in the operative position asshown, contact with a respective conductor through a corresponding slot 3. These strips 28 are distributed over the length of the support to provide insulation between the strips. The cross-section of each strip is sufficiently large for the anticipated current and the contact face of each strip is sufficiently narrow to ensure good contact with the respective circular conductor 15 under the bias of the corresponding spring 29. With a braided conductor 15, the strips 29 will slightly penetrate into the conductor so that a good contact is always provided. Preferably each strip 28 is a tight fit in the corresponding slot 3.

Referring now to the contact device of FIG. 6, the support 25 comprises a plate 30 and an upper part 31 (broken lines). The strips 28 have right angled bends so that parts 29 situated above the plate 30 act as biassing springs. At the free end of each part 29', a connecting screw 32 is provided. which can be connected for instance with a socket outlet or the like to be fixed on the upper part 31.

Between the parts 30 and 31 a longitudinally slidable rod 33 has been provided of which one end portion protrudes beyond these parts. The central portion of this rod 33 rests on the parts 29' and retains them in the position shown. Near each end of this rod at least one arm 34 engages in a recess in the rod and is rigid with a rotatable shaft 35 carrying a slamping projection 26 in the form of a cam. As shown in FIG. 6 the earns 26 are provided at one edge only, whereas the opposite edge of part 30 a shoulder 36 is provided which is urged against the opposite wall of the cable-duct when the cams 26 are turned outward. It is also possible to provide the cams 26 at both edges. Also, each shaft may carry two or more cams 26, depending on the shape of the applied profile. Moreover, the rod 33 may have wedge-shaped surfaces which urge the strips 28 downward during the locking operation in order to increase the contact pressure.

FIGS. 7 to 11 show a preferred embodiment of the contact device. The support means for the resiliently biased contact strips here comprises a rectangular plastics box like housing 37 having slots 27 in the bottom thereof. At the shorter end faces of the box 37 slightly resilient connection pieces 38 are provided, at the end of which clamping claws 39 are formed which carry the projections 26 and have holes 40. By inserting the noses of a pair of pliers in these holes the claws 39 may alternative embodiments.

The holder of FIG. 9A comprises a substantially U- section or a substantially C-section frame 43 and a slot 44 in the one leg into which a substantially T-shaped contact strip 28 can be inserted. A spring 29 rests against the cross-piece of the strip and is fixed to the frame 43 at the opposite end by means of a fixing screw 45 which also acts as a connection screw. when necessary an additional connection screw 45 can cooperate with this leg of the frame 43.

FIG. 9B shows an embodiment in which the crosspiece 28' of the contact-strip 28 is bent at right angles whereas the slot 44 is so disposed that this cross-piece can slide along the upright base part of the frame 43. The spring 29 takes the form of a hairpin-spring which is fixed to the one leg of the frame by means of the screw 45, and which rests at its other extremity, against the cross-pin 28', thus urging the latter against the con-' necting leg of the frame 43 and thereby guiding it.

FIGS. 10 and 11 show a complete support comprising, in addition to the box 37, an upper box 46 which is secured to the lower box by means of a dove-tail or other connection 47. The upper box is shallower near the connection with the lower box and is, there, subdivided by means of transverse partitions 48 into compartments 49 which correspond, in the assembled state, with the partitions 41 of the lower box. The partitions 41 have projecting ribs 50 fitting into corresponding grooves of of the partitions 48 of the upper box, as shown in FIG. 10B. Further, the partitions 48 have support-ribs 51 against which a contact-strip frame, mounted on the corresponding compartment of the lower box, can rest, so that these frames are held firmly and mutually insulated between the two boxes. As is apparent from FIG. 11, the box 46 is deeper alongside the cable duct 11, which deeper part can be used for effecting an electrical connection and to accommodate a socket outlet, switch or the like, which can be installed in a recessed mounting in a cover plate 52 of the box 46. It is also possible to mount such switching or contact means on the shallow part of the upper box in which case the deeper part can be omitted. Also the upper box can be made wider than the lower box in order to accommodate a number of such switching or contact means next to each other.

One side wall of the upper box 46 may be provided with opposed recesses 53, closed off by means of a frangible partition, through which conduit tubes or cables can be introduced. As the compartments 49 in the shallow part of the upper box 46 are in open connection with the interior of the deeper part, connecting wires can readily pass to the screws 45 of the frames 43, which screws, as is apparent from FIG. 11, protrude into the compartment 49 between the support ribs 51.

A complete connecting box into which the contact strips frames have been inserted, can be inserted in a cable-duct 11. When the lower box 37 is inserted into the space 16 of ,the cable duct, the contact strips 28 penetrate into the corresponding slots 3, whereby the springs 29 are compressed. The projections 26 then snap behind the longitudinal ribs 13 of the cable duct thus locking the box in the duct.

One of the contact strips is intended to form ground connection and it will be, preferably, made longer than the other contact strips in order to establish the ground connection earlier than the other connections and to maintain it longer at disassembly. It is also possible to place the frame 43 for the ground connection lower in the lower box 37 than the other frames, for example, by providing additional supports in the compartments for the other contact-strip frames.

When the cable duct 11 is constructed as a skirting board, as shown in FIG. 4, a plastics cover is used, which can easily be broken away over a length corresponding with the width of the lower box 37.

It will be appreciated that corner junction and branch pieces can be used by means of which different cableducts can be joined together, for example by means of interengaging snap connections.

The application of a flat cable according to FIGS. 1 and 2 can be considerably simplified when, as shown in FIGS. 12 and 13, the cover plate 5 is replaced bya cover layer 54, glued or welded at 55 to the top of the lower part 1, and made out of plastics with such characteristics that the contact strips 28 can be pressed through this layer without removing material, whereas, after withdrawing these contact-strips, the thus formed openings 56 substantially close up by the elasticity of the material as shown at 56 in FIG. 13. This is, in particular, advantageous when the connections with the conductors have to change position often, for example when the connection device forms part of a lampholder which, depending on the desired lighting effect, should be moved along a support or duct in which the cable is situated, as for example for illumination of exhibition and display rooms.

The hereinbefore described constructions provide an effective insulation and protection of conductors against corrosion. The base 1 can be used without a cable-duct or other cover. What we claim is:

1. A system for installing plural, preferably round conductors for establishing a cable as well as connections to the said conductors of the cable, comprising:

a flexible, elongated base element of rectangular cross section and made of electrically insulative material, the base having plural internal, parallel, longitudinal grooves individually receiving the con ductors, further having narrow slots communicating with and for access to said grooves and through which the condcutors pass when being placed into the grooves, the slots being narrower than the conductors;

a cable duct having U-shaped cross section receiving the base element in abutment with the base of the U, the inside of the legs of the U being provided with ribs behind which the base element rests when inserted into the duct, for retaining the base element in the duct, the said slots in the base element open to the open portion of the U, the legs of the U having additional ribs near or at the respective ends of the legs and facing each other;

support means received in said duct, above the base element therein, and having outwardly extending resilient positioning members which engage behind said additional ribs to retain the support means in the duct in definite position relative to the base element therein;

plural contact pins of rectangular cross section and having flat end faces held in the support means and extending therefrom, and having relative alignment with the conductors in the grooves of the base member; and

resilient means in the support means for urging the individual contact pins through the slots in said member and into contact making engagement with the respective conductors therein, and for maintaining said contact making engagement, the sides of said slots resiliently gripping said contact pins as they are inserted through said slots.

2. A system according to claim 1, further comprising an elongate cover hingedly connected to one longitudinal edge of the base element.

3. A casing according to claim 1 wherein at least one longitudinal edge of the base element has additional slots to augment the flexibility thereof.

4. A system according to claim 1, wherein the base element is provided with a cover, connected along one longitudianl edge thereof which can be held to the base adjacent the other longitudinal edge by snap connections means.

5. A system according to claim 2, wherein the cover is provided with a pulling lip which is arranged to rest against the side wall of the duct when the cover is closed.

6. A system according to claim 1 wherein the cable duct is an extruded plastics section.

7. A system according to claim 1 wherein the cable duct has at least one additional substantially C- or U.- section portion of which the base is formed by one leg of the main section.

8. A system according to claim 7, comprising a fixing component fitting into the additional C-section portion, the length of which component is not smaller than the largest interior width of the C-section, whereas the width of said component is'smaller than the width of the opening of this section, which component is or can be connected either to a suspension rod or to a fixingscrew for a cover plate for the cable duct.

9. A system according to claim 1, wherein said resilient positioning members comprise pairs of resilient claws which are movable inwardly to free the support from the duct.

10. A system according to claim 9, wherein the claws have an opening into which the noses of a pair of pliers can be inserted so as to move the claws inwardly.

11. A system as in claim 2, the support means including a box-like housing having slots through which the contact pins extend, and contact pin holders in said housing, each for holding one of said contact pins in position for traversing the respective slots in the housing and a respective aligned one of said slots in the base element.

12. A system according to claim 11, wherein the said base member is provided with a plastic material covering the face thereof at the side to which the longitudinal grooves and slots open. a

13. A system according to claim 4, wherein said snap action means comprises a beaded longitudinal rib on the cover and arranged to engage in a complementary longitudinal additional groove in the base member when the cover is closed. 1

14. A system according to claim 1, and including individual holders for each contact pin, said resilient means including individual resilient elements, each contact pin being resiliently supported in the respective holder by the respective resilient element, each said holder being releasably connected to the support.

15. A system as in claim 1, said support means including a bar with a plurality of apertures, each receiving one of said electrical contact pins; said resilient means being springs on the bar for biasing the contact pins into engagement with the respective conductors in the grooves.

16. A system according to claim 1, wherein the said support means is of substantially rectangular contour of which the width is not larger than the width of the U- opening in the cable duct, said support means having a plurality of rectangular section slots distributed over the length of the support means, the longitudinal axis of each slot extending substantially parallel to the longitudinal dimension of the support means, and which slots are so staggered transversely that each one is located opposite a conductor of the base member when the support means as disposed in the duct, said contact pins being strips and resiliently supported in the respective slots.

17. A system according to claim 11, comprising a dove-tail connection between the first and the second components.

18. A system according to claim 16, wherein the support means comprises a first and second component, the first component carrying the resilient positioning members and the contact strips, the second component being detachably secured to the first component and including oppositely directed support parts for the first component.

19. A system as in claim 1 l, the resilient means being plural springs, respectively held by and bearing against a contact pin holder.-

20. A system as in claim 18, including partitions in the housing to subdivide the space therein and to separate the holders therein from each other.

21. A system according tol claim 12, wherein the plastics material has such characteristics that it is being pierced by a contact pin without appreciably removing material of the layer, whereby the thus-formed opening will substantially close up after withdrawal of the contact pin.

22. A system according to claim 1, wherein said resilient positioning members include clamping claws and a longitudinally slidable rod by means of which the clamping claws as situated near longitudinal sides of the support means can be turned outward to engage the sides of the cable duct.

23. A system according to claim 13, wherein the rod is provided with cams by means of which the contact strips are biassed towards the support means when the claws are turned outwardly.

24. A system as in claim 14, wherein each holder consists of a substantially C-shaped or U-shaped frame and being provided with connection means, each contact pin being a strip protruding through a slot in a leg of the respective frame, and wherein said resilient elements are springs, respectively acting between the opposite leg of the frame and a cross-piece of the contact strip.

25. A system according to claim 14, wherein the cross-piece of said contact strip extends at right angles to the main part thereof and can slide along an adjacent connecting leg of the frame, the spring being a hairpin spring which exerts a bias on the cross-piece towards this connecting leg.

26. A system according to claim 22, wherein the contact pins are resilient strips and are so shaped that they extend substantially at right angles above the support means, and the parts extending above the support means are maintained in position under the rod and act as springs for biasing these parts of the strips as extending beyond the rod.

27. A system according to claim 1, wherein one of said contact pins is provided to establish a connection with a ground conductor of the cable, before the coupling operation of the contact device with a duct, and

protrudes farther outward than the other contact pins. l l 

1. A system for installing plural, preferably round conductors for establishing a cable as well as connections to the said conductors of the cable, comprising: a flexible, elongated base element of rectangular cross section and made of electrically insulative material, the base having plural internal, parallel, longitudinal grooves individually receiving the conductors, further having narrow slots communicating with and for access to said grooves and through which the condcutors pass when being placed into the grooves, the slots being narrower than the conductors; a cable duct having U-shaped cross section receiving the base element in abutment with the base of the U, the inside of the legs of the U being provided with ribs behind which the base element rests when inserted into the duct, for retaining the base element in the duct, the said slots in the base element open to the open portion of the U, the legs of the U having additional ribs near or at the respective ends of the legs and facing each other; support means received in said duct, above the base element therein, and having outwardly extending resilient positioning members which engage behind said additional ribs to retain the support means in the duct in definite position relative to the base element therein; plural contact pins of rectangular cross section and having flat end faces held in the support means and extending therefrom, and having relative alignment with the conductors in the grooves of the base member; and resilient means in the support means for urging the individual contact pins through the slots in said member and into contact making engagement with the respective conductors therein, and for maintaining said contact making engagement, the sides of said slots resiliently gripping said contact pins as they are inserted through said slots.
 2. A system according to claim 1, further comprising an elongate cover hingedlY connected to one longitudinal edge of the base element.
 3. A casing according to claim 1 wherein at least one longitudinal edge of the base element has additional slots to augment the flexibility thereof.
 4. A system according to claim 1, wherein the base element is provided with a cover, connected along one longitudianl edge thereof which can be held to the base adjacent the other longitudinal edge by snap connections means.
 5. A system according to claim 2, wherein the cover is provided with a pulling lip which is arranged to rest against the side wall of the duct when the cover is closed.
 6. A system according to claim 1 wherein the cable duct is an extruded plastics section.
 7. A system according to claim 1 wherein the cable duct has at least one additional substantially C- or U-section portion of which the base is formed by one leg of the main section.
 8. A system according to claim 7, comprising a fixing component fitting into the additional C-section portion, the length of which component is not smaller than the largest interior width of the C-section, whereas the width of said component is smaller than the width of the opening of this section, which component is or can be connected either to a suspension rod or to a fixing-screw for a cover plate for the cable duct.
 9. A system according to claim 1, wherein said resilient positioning members comprise pairs of resilient claws which are movable inwardly to free the support from the duct.
 10. A system according to claim 9, wherein the claws have an opening into which the noses of a pair of pliers can be inserted so as to move the claws inwardly.
 11. A system as in claim 2, the support means including a box-like housing having slots through which the contact pins extend, and contact pin holders in said housing, each for holding one of said contact pins in position for traversing the respective slots in the housing and a respective aligned one of said slots in the base element.
 12. A system according to claim 11, wherein the said base member is provided with a plastic material covering the face thereof at the side to which the longitudinal grooves and slots open.
 13. A system according to claim 4, wherein said snap action means comprises a beaded longitudinal rib on the cover and arranged to engage in a complementary longitudinal additional groove in the base member when the cover is closed.
 14. A system according to claim 1, and including individual holders for each contact pin, said resilient means including individual resilient elements, each contact pin being resiliently supported in the respective holder by the respective resilient element, each said holder being releasably connected to the support.
 15. A system as in claim 1, said support means including a bar with a plurality of apertures, each receiving one of said electrical contact pins; said resilient means being springs on the bar for biasing the contact pins into engagement with the respective conductors in the grooves.
 16. A system according to claim 1, wherein the said support means is of substantially rectangular contour of which the width is not larger than the width of the U- opening in the cable duct, said support means having a plurality of rectangular section slots distributed over the length of the support means, the longitudinal axis of each slot extending substantially parallel to the longitudinal dimension of the support means, and which slots are so staggered transversely that each one is located opposite a conductor of the base member when the support means as disposed in the duct, said contact pins being strips and resiliently supported in the respective slots.
 17. A system according to claim 11, comprising a dove-tail connection between the first and the second components.
 18. A system according to claim 16, wherein the support means comprises a first and second component, the first component carrying the resilient positioning members and the contact strips, the sEcond component being detachably secured to the first component and including oppositely directed support parts for the first component.
 19. A system as in claim 11, the resilient means being plural springs, respectively held by and bearing against a contact pin holder.
 20. A system as in claim 18, including partitions in the housing to subdivide the space therein and to separate the holders therein from each other.
 21. A system according to claim 12, wherein the plastics material has such characteristics that it is being pierced by a contact pin without appreciably removing material of the layer, whereby the thus-formed opening will substantially close up after withdrawal of the contact pin.
 22. A system according to claim 1, wherein said resilient positioning members include clamping claws and a longitudinally slidable rod by means of which the clamping claws as situated near longitudinal sides of the support means can be turned outward to engage the sides of the cable duct.
 23. A system according to claim 13, wherein the rod is provided with cams by means of which the contact strips are biassed towards the support means when the claws are turned outwardly.
 24. A system as in claim 14, wherein each holder consists of a substantially C-shaped or U-shaped frame and being provided with connection means, each contact pin being a strip protruding through a slot in a leg of the respective frame, and wherein said resilient elements are springs, respectively acting between the opposite leg of the frame and a cross-piece of the contact strip.
 25. A system according to claim 14, wherein the cross-piece of said contact strip extends at right angles to the main part thereof and can slide along an adjacent connecting leg of the frame, the spring being a hairpin spring which exerts a bias on the cross-piece towards this connecting leg.
 26. A system according to claim 22, wherein the contact pins are resilient strips and are so shaped that they extend substantially at right angles above the support means, and the parts extending above the support means are maintained in position under the rod and act as springs for biasing these parts of the strips as extending beyond the rod.
 27. A system according to claim 1, wherein one of said contact pins is provided to establish a connection with a ground conductor of the cable, before the coupling operation of the contact device with a duct, and protrudes farther outward than the other contact pins. 